# Homework Help: Friction Problem -- String is tied to a block and a hanging bucket

1. Nov 19, 2014

### Nithya115

USE OF THE PHYSICS FORUMS TEMPLATE IS REQUIRED ON ALL HOMEWORK PROBLEMS. PLEASE COMPLY WITH THIS IN THE FUTURE.

A string is tied to a 4.4 kg block and 120g hanging bucket. Students add 20g washers one at a time to the bucket. The student are unaware that the

coefficient of static friction for the block on the table is 0.42.
A) what is the maximum force of static friction for the block?
B) how many washers can the students add to the bucket without moving the block?
C) the coefficient on kinetic friction is 0.34. Calculate the acceleration of the block when the final washer is added to the bucket and the objects start to move...

How do get c)? I got 0.56m/s^2 but the answer in the book is 0.75m/s^2

Last edited by a moderator: Nov 19, 2014
2. Nov 19, 2014

### Staff: Mentor

Is it correct to assume that there is a pulley present somewhere?

Chet

3. Nov 19, 2014

### Nithya115

ya there is a pulley between the bucket and the block. Basically, the block is sitting on the table and there is a pulley at the edge of the table. The bucket is hanging from the string that is on the pulley. its like the usual diagrams.

I also did the same procedure but I am not getting that answer!

Last edited: Nov 19, 2014
4. Nov 19, 2014

### Staff: Mentor

Chet

5. Nov 19, 2014

### Nithya115

a= m2g -Fs/ m1 + m2
a= (1.86 x 9.8) - 15/ (4.4 + 1.86)
a= 0.52m/s^2

I got Fs by...
Fs = (0.34)(Fn=4.4x9.8)
= 1.86

I got m2 by...
1. calculating the mass of the washers
20g x 87 washers = 1740g
2. adding the bucket and washers
120g + 1740g = 1860g
3. converted to kg
1860g/1000g=1.86 kg

6. Nov 19, 2014

### Staff: Mentor

Your methodology is solid. I get 0.57 m/s2, in rough agreement with your 0.56. The book shows 0.75, but they got the digits interchanged. For the kinetic friction force, I got 14.7 N.

Chet

7. Nov 19, 2014

### Brul

Just a second confirmation; I get 0.58 m/s2 as well.

8. Nov 19, 2014

### Staff: Mentor

Hi Brul. Welcome to Physics Forums.

Chet

9. Nov 19, 2014

### Brul

Hello and thank you!

10. Nov 19, 2014

### Nithya115

Thanks. I rounded the kinetic force to 15 which I probably should avoid.